Electrolytic cell

ABSTRACT

A cell for electrolytic recovery of metals from a slurry in which the cathode is a hollow rotor, the walls of which define a regular polygon. The rotor is mounted concentrically within a polygonal shaped tank, the inner walls of which are lined with suitable material to function as the anode. The cathode rotor is journalled for rotation and is oscillated through a substantial arc within the tank. The cathode rotor comprises an insulated frame and each of its several sides supports a removable cathode plate. Each cathode plate is held in the insulating frame by slots or grooves in the peripheral frame members into which the bottom and side edges of the plate fit. Narrow elongated baffle strips are mounted on the frame in spaced parallel relationship to the junction line where the side and bottom edges of cathode plates enter the slots. The baffle strips are of non-conductive material and are located between the junction lines and the anode surface of the tank wall. These strips provide a barrier to lineof-sight current between the anode and the junction lines thereby avoiding current peaks and undesirable buildup of dendritic metal deposits at the edges of the cathode plates. The baffle strips also direct the electrolyte in a scouring stream against the face of the oscillating cathode to break up potential polarization. Scoop-like baffles are also provided adjacent the bottom corner of the cathode plates. The scoops face each other so that one scoop pumps the electrolyte slurry upwardly when the cathode rotor oscillates in one direction and the other scoop pumps the electrolyte-slurry mixture upwardly during reverse oscillation. The tank may be formed as an annular vessel with both its inner and outer walls acting as anodes and the cathode rotor is suspended to oscillate between the walls.

United States Patent m1 G00ld et al.

l ELECTROLYTIC CELL [7S] lnventors: Reed Goold: Charles W. Wojcik,

both of Twin Falls; Gerald D. Cooper, Pocatello. all of ldaho [73] Assignee: Wilfred H. Herrett, Filer, Idaho a part interest 22 Filed: Feb. 25, 1974 211 Appl. No.: 444,784

Related US. Application Data [03] Continuation-in-part of Serf No 288.771, Sept. 13.

1972. Pat. No. 3.800434.

545.328 8/1895 Wiggin r 4 r r a .0 204/222 X 791.341 5/1905 Harrison et 204/237 X 1028285 1/1936 Jephson et 111....204/212 X 3507.770 4/1970 Fleming 204/106 X Primary Examinerjohn H. Mack Assistant Eruminer-Aaron Weisstuch [57] ABSTRACT A cell for electrolytic recovery of metals from a slurry in which the cathode is a hollow rotor, the walls of which define a regular polygon. The rotor is mounted 1 1 NOV. 11, 1975 concentrically within a polygonal shaped tank. the inner walls of which are lined with suitable material to function as the anode The cathode rotor is journalled for rotation and is oscillated through a substantial are within the tank The cathode rotor comprises an insu lated frame and each of its several sides supports a removable cathode plate. Each cathode plate is held in the insulating frame by slots or grooves in the periph' eral frame members into which the bottom and side edges of the plate fit. Narrow elongated baffle strips are mounted on the frame in spaced parallel relation ship to the junction line where the side and bottom edges of cathode plates enter the slots. The baffle strips are of non-conductive material and are located between the junction lines and the anode surface of the tank wall These strips provide a barrier to line-ofsight current between the anode and the junction lines thereby avoiding current peaks and undesirable buildup of dendritic metal deposits at the edges of the cathode plates The baffle strips also direct the elec trolyte in a scouring stream against the face of the os cillating cathode to break up potential polarization. Scoop-like battles are also provided adjacent the bottom corner of the cathode plates The scoops face each other so that one scoop pumps the electrolyte slurry upwardly when the cathode rotor oscillates in one direction and the other scoop pumps the elec trolyte-slurry mixture upwardly during reverse oscillation. The tank may be formed as an annular vessel with both its inner and outer walls acting as anodes and the cathode rotor is suspended to oscillate between the walls.

5 Claims, 8 Drawing Figures llun lunnnlullll WW w" u 111 11 1 ll lll l "Hu p num l8 US. Patent Nov. 11, 1975 Sheet 1 of2 3,919,070

" um anw'w WIN US. Patent Nov.11, 1975 Sheet2of2 3,919,070

ELECTROLYTIC CELL RELATIONSHIP TO OTHER APPLICATIONS This application is a continuation-in-part of copending application Ser. No. 288,77] filed Sept. I3, 1972 now U.S. Pat. No. 3,806,434, for APPARATUS AND METHOD FOR ELECTROLYTIC RECOVERY OF METALS.

BACKGROUND OF THE INVENTION This invention relates to the electrolytic recovery of metals from crushed metal-bearing ores and/or concentrates and provides improved ways and means for effecting such recovery directly from crushed ores or concentrates without prior leaching and at current densities well over 100 amperes per square foot of cathode area.

Our co-pending application discloses and claims apparatus in which the cell tank is an annular channel shaped as a regular polygon. The inner surfaces of the tank are lined with conductive material and form one of the electrodes, preferably the anode. The other electrode, preferably the cathode, is a hollow rotor, the walls of which define a regular polygon of the same number of sides as the tank and is mounted for oscillating movement. The rotor is positioned so that its wall is suspended midway between the cell walls. The anode and cathode are separately connected to suitable poles of a direct current source, the cell is filled with a slurry of crushed ore in electrolyte arid the cathode is oscillated in the cell. With such apparatus, high current densities, in excess of 50 amp/ft", have been employed to effect recovery of high purity high density metals, such as copper, silver and gold at current efficiencies above 90%. With this system, we are able to operate at current densities up to 100 amp/ft with consistent success; however, at current densities above that level, buildup of dendritic metal adjacent the edges of the individual cathode plates and even on the face of the cathode was experienced. This is probably due to polarization, but whatever the cause, it limits the capacity of the cell to that attainable at current density levels below that at which dendrites form under prevailing conditions.

SUMMARY OF THE INVENTION It is the primary object of the present invention to provide ways and means to enable the use in electrolytic cells of high current densities, well above 100 amp/ft of cathode area, yet avoid undesirable polarization at the cathode with its resultant dendrite formation either adjacent the cathode edges or on cathode surface.

Another object is to provide, for use in a cell having an oscillating cathode, an improved structure that shades the cathode edges while providing a more positive scrubbing action across the cathode surface thereby in both instances preventing polarization and undesirable dendrite formation.

A further object is the provision of a cathode rotor structure that enhances scrubbing of the cathode and agitation of the slurry to maintain it as a uniformly mixed suspension.

BRIEF DESCRIPTION OF THE DRAWINGS In order that the invention may be more readily understood and carried into effect, reference is made to the accompanying drawings and description thereof which are offered by way of illustration only and not in limitation of the invention, the scope of which is defined solely by the appended claims and equivalents.

FIG. I is a top view of an electrolytic cell embodying the invention, certain parts being cut away for purposes of clarity.

FIG. 2 is a side elevation view of the cell illustrated in FIG. 1.

FIG. 3 is a sectional view taken in the plane of line 3-3 of FIG. 1 looking in the direction of the arrows 3.

FIG. 4 is a sectional view taken in the plane of lines 44 of FIG. 2 looking in the direction of the arrows 4.

FIG. 5 is a top view of a portion of the cathode rotor employed in the cell.

FIG. 6 is an enlarged view of the circled portion of FIG. 5.

FIG. 7 is a partial side view of the rotor of the cell showing one complete and two partial cathode panels with supporting structure, a portion being cut away for purposes of clarity.

FIG. 8 is a sectional view of the cathode rotor structure taken in the plane of line 8-8 of FIG. 6 looking in the direction of arrows 8.

DESCRIPTION OF THE PREFERRED EMBODIMENT The illustrated embodiment comprises a tank 10 having a bottom 11 and formed as an annular trough between inner and outer side walls 12 and 13 which define a regular octagon. The sidewalls 12 and 13 serve as anodes and to this end are faced on their inner surfaces with a continuous conductive liner 14 of suitable anode material, such as an antimony-lead alloy. The anodes connect by means of lugs and bars 16 to the positive pole of a suitable direct current source not shown. The structural walls 12 and 13 are of a suitable non-conductive material, such as polypropylene.

The tank bottom 11 rests on a frame comprising legs 17 and cross beams 18. Any suitable feed and discharge arrangement may be employed to maintain a desired level of slurry in the tank.

Secured on a lower cross beam 18 is a combination radial and thrust bearing 21 (FIG. 3) on which is fitted a vertical shaft 22 thereby supporting the shaft and journalling it for rotation. The shaft is also journalled for rotation in a second bearing 23 that mounts on the tank base 11 thereby steadying the shaft. A sprocket 24 is fixed to the shaft adjacent its lower end. A suitable reversible hydraulic motor 26 is mounted on a lower cross beam 18 (FIG. 4) and is provided with a sprocket 27 that engages a chain 28 trained about both sprockets 24 and 27. A lug 29 is secured on the chain in position to alternately actuate micro-switches 31 which in turn operate solenoid valves (not shown) in the hydraulic supply hoses 33 to reverse the flow of pressured hydraulic fluid directed to the motor via such hoses thereby to reverse the motor and shaft in known manner. The switches 31 and lug 29 are spaced to effect about a oscillation of the shaft and of a rotor 34 (FIGS 1 and 2) that is secured to the upper end of the shaft 22 above the tank. If desired, other forms of drive, such as gears or rams, may be employed.

The rotor 34 comprises a top plate 36 shaped as a regular octagon with a frame of vertical members 37 (FIGS. 3 and 5) depending from each corner into the annular tank between the walls 12 and 13. Each pair of adjacent vertical frame pieces are joined together at the bottom by a transverse horizontal cross frame member 38. For added strength adjacent bottom cross members are joined together so that the bottom of the rotor frame is continuous. The top plate 36 and the frame members are all non-conductive and may be formed from polypropylene or rubber covered steel.

Slots 39 are milled into the inside or facing edges of the frame pieces 37 (FlG. 8) and the top edge of the cross member 38 to accept the side and bottom edges of a cathode plate 41 to removably support the plate as one wall of the cathode. The plate should fit snugly into the slots to minimize metal deposition on the plate edge. A junction line 40 exists along the edges of the slots where the plate enters the slots. The cathode plates may be of any suitable metal. We have found titanium and stainless steel to be especially durable.

Each cathode plate 41 has an upper flange 42 (FIG. 8) that is bored to fit over studs 43 and be secured thereto in contact with a cable 44 by suitable nuts. The cable 44 passes downwardly through the hollow shaft 22 (FIG. 3) to eventual connection to the negative pole of a DC. source not shown. When all cathode plates are fitted into place, the basic cathode rotor thus formed comprises the top and a depending skirt wall, including cathode plates 41 that extends into the tank between and concentric with the inner and outer tank walls.

In order to avoid polarization on the face of the cathode plates as well as adjacent the edges, the cathode rotor is equipped with a series of baffle strips of particular location.

As best illustrated in FIGS. -7, for each cathode plate the arrangement includes a pair of elongated vertical baffle strips 46 and a bottom transverse strip 47. The strips are mounted on spacers 48 which hold them in spaced apart parallel relationship to the frame and to the junction line 40 where the cathode plate enters the slots 39. The strips are positioned to extend on both sides of such junction line. Only a few spacers 48 are used as it is necessary to have free flow of the electrolyte slurry between the strips and the cathode. The baffle strips, which are non-conductive, shadow the junction line by providing a barrier to line-of-sight current flow between the junction line and anode liner of the tank. Current can flow only circuitously through the electrolyte around the baffle. As the rotor oscillates the flat strips also serve to direct the slurry onto and across the face of the cathode thus effecting a scrubbing action that prevents or breaks up polarization and thus avoids undesirable dendrite formation.

An additional scrubbing and stirring action is achieved by curved scoops 51 located adjacent at least one, preferably both, bottom corners of each cathode plate. The scoops face each other and curve from a substantially horizontal portion below the cathode to an upper substantially vertical portion that terminates at or below the transverse junction line 40. If the scoop extends above this junction line there will be insufficient scrubbing action across the lower part of the plate and destructive polarization will occur. Like the baffle strips and frame, the scoops are formed from nonconductive material.

So far as the electrolyte slurry flow is concerned, orientation of the baffle strips will be achieved empirically depending on the size and speed of the rotor as well as the material being handled. Usually good results will be obtained with the strip aimed to direct the slurry toward the plate surface at or inboard of the opposite junction line 40. The baffles should be spaced outwardly from the frame to 1 inch.

It is important that adjacent baffle strips be located to maximize slurry flow behind the baffle and across the plate as the rotor oscillates. As best shown in FIG. 6, the baffle strips 46 on the outer walls of the rotor are spaced apart and each is slightly angled toward the surface ofthe plate with which it is associated. Slurry passing under the strip as the rotor oscillates probably comes partly from (a) slurry pumped upwardly by the scoops 51, (b) slurry flowing from the surrounding tank contents into spaces between the baffles and (c) slurry already close to the cathode plates.

The strips associated with the inside of the rotor are arranged to accommodate the reduced space available there. In this connection, it will be remembered that to perform the shadow function, the strips must be positioned so that they extend on both sides of the junction line 40. In order to meet this requirement and still insure proper flow, adjacent vertical baffle strips 46 on the inside of the rotor are arranged so that one angles to a spaced but overlapping relationship to its adjacent strip. Thus, as the rotor oscillates in one direction a positive scooping of fresh slurry onto the cathode is effected by the overlapping baffle and when oscillation is reversed scrubbing is achieved by moving the cathode past the slurry already against the inner cathode surfaces as well as by the slurry directed upwardly by the scoops 51 which, it should be noted, are of sufficient width to pump slurry upwardly under the strips 46 on both sides of the cathode plates.

To enhance rotor stability, a plurality of rigid vertical posts 52 (FIG. 3) are welded to the inner wall of the shaft adjacent its top and extend upwardly therefrom to support a cap 53 from which a plurality of guy rods 54 extend to connect at each corner of the top plate 36 of the rotor.

Although the cell and rotor have been described with reference to those shaped as an octagon structure, the invention has broad application to oscillating cathodes in which immersed edges of individual cathode plates must be shadowed to block edge polarization. Thus, a regular polygon of any number of sides may embody the invention. Also, the tank need not be an annulus, but may be constructed as an open vessel with only the outer wall as an anode. In general, however, the annular form is preferred because it increases the anode area and puts an anode on both sides of each cathode plate.

The baffle strips have enabled use of much higher current densities than the same cell without such baffles. For instance, in a given cell without the strips, dendrite formation became pronounced at lOO amp/ft when treating an oxide copper. In the same cell, fitted with baffle strips according to this invention, the same oxide copper was treated under the same general conditions yet current densities as high as 200 amp/ft could be employed without dendrite formation and the resulting product was a high quality copper recovered at increased rates.

We claim:

1. An electrolytic cell, comprising a polygonal shaped tank having its inner sidewall surfaces lined with conductive material enabling it to function as an anode; a cathode rotor located concentrically within said tank; means mounting said cathode rotor for oscillation within said tank; said cathode rotor comprising a top and a depending sidewall, said sidewall comprising a non-conductive frame and a plurality of conductive cathode plates supported in said frame, said frame comprising a plurality of equally spaced vertical members and transverse members connecting the bottom ends of adjacent ones of said vertical members, slots adapted to receive the side and bottom edges of said cathode plates in the facing edges of said vertical members and the top edge of said transverse members, said plates and slots forming junction lines where said plates enter said slots; means for connecting said tank wall lining and said cathode plates respectively to the positive and negative poles of a direct current source; and means for shading said junction lines from line-of-sight current flow between said tank wall liner and said cathode, said means comprising for each of said junction lines an elongated strip of non-conductive material of length at least equal to the length of the junction line with which it is associated and of width to extend on both sides of said junction line, and means mounting said strip to said frame in spaced parallel relationship therewith and between said junction line and said tank wall.

2. The electrolytic cell according to claim I with the addition of a curved baffle adjacent at least one bottom corner of each cathode plae, said baffle being curved to extend from a horizontal portion beneath one of said cathode plates to terminate in a vertical portion adjacent the side of said one cathode plate at an elevation approximate the elevation of the junction line defined by the bottom of said cathode plate with said transverse frame member.

3. The electrolytic cell according to claim 2 in which there are provided two curved baffles for each cathode plate, each one of said baffles being located adjacent an opposite edge of said cathode plate with their respective horizontal end portions beneath said cathode plate.

4. The electrolytic cell according to claim I in which said cathode rotor is a polygon of sides equal in number to said tank and each of said sides includes one of said cathode plates.

5. An electrolytic cell according to claim I in which said tank is formed as an annular vessel defined by inner as well as outer walls defining polygons, both said inner and outer walls are lined with conductive material and means are provided for connecting said conductive material to the positive pole of a source of direct current, and said means mounting said cathode rotor for oscillation comprises a rotatably journalled vertical shaft axially aligned with the center of said tank, means securing said cathode rotor to said shaft and drive means for oscillating said shaft.

* i l l 

1. AN ELECTROLYTIC CELL, COMPRISING A POLYGONAL CHAPED TANK HAVING ITS INNER SIDEWALL SURFACES LINED WITH CONDUCTIVE MATERIAL ENABLING IT TO FUNCTION AS AN ANODE, A CATHODE ROTOR LOCATED CONCENTRICALLY WITHIN SAID TANK, MEANS MOUNTING SAID CATHODE ROTOR FOR OSCILLATION WITHIN SAID TANK, SAID CATHODE ROTOR COMPRISING A TOP AND A DEPENDING SIDEWALL, SAID SIDEWALL COMPRISING A NON-CONDUCTIVE FRAME AND A PLURALITY OF CONDUCTIVE CATHODE PLATES SUPPORTED IN SAID FRAME, SAID FRAME COMPRISING A PLURALITY OF EQUALLY SPACED VERTICAL MEMBERS AND TRANSVERSE MEMBERS CONNECTING THE BOTTOM ENDS OF ADJACENT ONES OF SAID VERTICAL MEMBERS, SLOTS ADAPTED TO RECEIVE THE SIDE AND BOTTOM EDGES OF SAID CATHODE PLATES IN THE FACING EDGES OF SAID VERTICAL MEMBERS AND THE TOP EDGE OF SAID TRANSVERSE MEMBERS, SAID PLATES AND SLOTS FORMING JUNCTION LINES WHERE SAID PLATES ENTER SAID SLOTS, MEANS FOR CONNECTING SAID TANK WALL LINING AND SAID CATHODE PLATES RESPECTIVELY TO THE POSITIVE AND NEGATIVE POLES OF A DIRECT CURRENT SOURCE, AND MEANS FOR SHADING SAID JUNCTION LINES FROM LINE-OF-SIGHT CURRENT FLOW BETWEEN SAID TANK WALL LINER AND SAID CATHODE, SAID MEANS COMPRISING FOR EACH OF SAID JUNCTION LINES AN ELONGATED STRIP OF NON-CONDUCTIVE MATERIAL OF LENGTH AT LEAST EQUAL TO THE LENGTH OF THE JUNCTION LINE WITH WHICH IT IS ASSOCIATED AND OF WIDTH TO EXTEND ON BOTH SIDES OF SAID JUNCTION LINE, AND MEANS MOUNTING SAID STRIP TO SAID FRAME IN SPACED PARALLEL RELATIONSHIP THEREWITH AND BETWEEN SAID JUNCTION LINE AND SAID TANK WALL
 2. THE ELECTROLYTIC CELL ACCORDING TO CLAIM 1 WITH THE ADDITION OF A CURVED BAFFLE ADJACENT AT LEAST ONE BOTTOM CORNER OF EACH CATHODE PLAE, SAID BAFFLE BEING CURVED TO EXTEND FROM A HORIZONTAL PORTION BENEATH ONE OF SAID CATHODE PLATES TO TERMINATE IN A VERTICAL PORTION ADJACENT THE SIDE OF SAID ONE CATHODE PLATE AT AN ELEVATION APPROXIMATE THE ELEVATION OF THE JUNCTION LINE DEFINED BY THE BOTTOM OF SAID CATHODE PLATE WITH SAID TRANSVERSE
 3. The electrolytic cell according to claim 2 in which there are provided two curved baffles for each cathode plate, each one of said baffles being located adjacent an opposite edge of said cathode plate with their respective horizontal end portions beneath said cathode plate.
 4. The electrolytic cell according to claim 1 in which said cathode rotor is a polygon of sides equal in number to said tank and each of said sides includes one of said cathode plates.
 5. An electrolytic cell according to claim 1 in which said tank is formed as an annular vessel defined by inner as well as outer walls defining polygons, both said inner and outer walls are lined with conductive material and means are provided for connecting said conductive material to the positive pole of a source of direct current, and said means mounting said cathode rotor for oscillation comprises a rotatably journalled vertical shaft axially aligned with the center of said tank, means securing said cathode rotor to said shaft and drive means for oscillating said shaft. 